Internal combustion engines, for example of the gasoline type, with turbo supercharging, have the tendency to knock as the motor temperature increases. The tendency to knock is particularly serious upon substantial increase in engine operating temperature which, in turbo-charged engines, may readily occur due to the high degree of filling of the cylinders with combustible fuel-air mixture in accordance with the supercharging by the turbo charger. It has previously been proposed to prevent knocking of the engine by retarding the ignition timing (see, for example, German Patent Disclosure Document DE-OS No. 28 01 512 or DE-OS 26 59 239 to which U.S. Pat. No. 4,133,475 and 4,002,155 correspond). Many types of internal combustion (IC) engines, and particularly turbo-charged engines, then will have exhaust which is excessively hot, and cause excessive heating of the turbo charger. This is undesirable due to the resulting decrease in power and efficiency. It is also possible in turbo-charged motors to decrease the charge in pressure which, however, also decreases the power output.